The present invention is directed in general to communication systems and, more particularly, to a direction sensitive coupling unit, for use in a local area network, to indicate the source direction of network transmissions.
Local area network is a tern used to define the systems and protocols (hardware and software) for interconnecting a multiplicity of autonomous computing devices in an office, building, or manufacturing environment. Typically, a plurality of computing devices, or users, are coupled to a common transmission medium via a bus interface unit (BIU). The BIU is provided to receive messages from the user and thereafter transmit these messages to other BIUs via the transmission medium in accordance with the network protocol.
Several standard local area network protocols now in use require a BIU to monitor the transmission medium to ascertain its status. For example, contention networks require the BIUs thereof to monitor the transmission medium to ascertain whether another BIU is transmitting. Similarly, token passing networks require the BIU to monitor the transmission medium to ascertain whether activity occurs within a predetermined interval. However, these standard protocols do not require the BIUs to determine the source direction of transmissions. Accordingly, prior art systems provide no apparatus for performing this task.
Nonetheless, there exists a need for apparatus, for use with a BIU, to ascertain the source direction of local area network transmissions in addition to ascertaining when information is being transmitted via the medium. This information could be used for improving existing protocols as well as providing new protocols. As an example, information indicating the source direction of network transmissions could be used in contention networks for resolving conflicts occurring therein. In such a protocol, whenever a conflict occurs, the BIU attempting transmission from a predetermined direction could, for example, "win" the conflict and continue transmitting. This is in contrast to existing contention networks wherein conflict is resolved by each BIU involved in the conflict terminating its transmission and remaining idle for a time period of random duration before attempting to retransmit.
Other uses for information regarding the source direction of transmissions in a local area network will become apparent to those skilled in the art.
One difficultly encountered in determining the source direction of transmissions in a local area network is that the nature of the transmission signal does not indicate its source direction. This situation is to be distinguished from that encountered in other types of communication systems. For example, in power distribution line systems, communication signals are transmitted over the power lines and include some characteristic, e.g., carrier frequency, data sequence, etc., that is specific to the source direction. In such a system, source direction may be ascertained by evaluating the direction specific characteristic of the signal.